Galileo described his famous inclined-plane experiment thus [from Day Three of Two New Sciences]:

"A piece of wooden moulding or scantling, about 12 cubits long, half a cubit wide, and three finger-breadths thick, was taken; on its edge was cut a channel a little more than one finger in breadth; having made this groove very straight, smooth, and polished, and having lined it with parchment, also as smooth and polished as possible, we rolled along it a hard, smooth, and very round bronze ball. Having placed this board in a sloping position, by lifting one end some one or two cubits above the other, we rolled the ball, as I was just saying, along the channel, noting, in a manner presently to be described, the time required to make the descent. We repeated this experiment more than once in order to measure the time with an accuracy such that the deviation between two observations never exceeded one-tenth of a pulse-beat. Having performed this operation and having assured ourselves of its reliability, we now rolled the ball only one-quarter the length of the channel; and having measured the time of its descent, we found it precisely one-half of the former. Next we tried other distances, comparing the time for the whole length with that for the half, or with that for two-thirds, or three-fourths, or indeed for any fraction; in such experiments, repeated a full hundred times, we always found that the spaces traversed were to each other as the squares of the times, and this was true for all inclinations of the plane, i. e., of the channel, along which we rolled the ball. We also observed that the times of descent, for various inclinations of the plane, bore to one another precisely that ratio which, as we shall see later, the Author had predicted and demonstrated for them.

"For the measurement of time, we employed a large vessel of water placed in an elevated position; to the bottom of this vessel was soldered a pipe of small diameter giving a thin jet of water, which we collected in a small glass during the time of each descent, whether for the whole length of the channel or for a part of its length; the water thus collected was weighed, after each descent, on a very accurate balance; the differences and ratios of these weights gave us the differences and ratios of the times, and this with such accuracy that although the operation was repeated many, many times, there was no appreciable discrepancy in the results."

This description seems straightforward enough to permit a fairly exact replication, and many people, probably in the thousands, have indeed replicated it over the centuries.

Jim Morris with the inclined-plane replica (diachronic in accuracy, cenochronic in spirit) that he and his wife Rhoda constructed.
[Antiques of Science & Technology]

A few of these re-enactors have been historians (as described in Part Two of this series). Their goal has been to re-create Galileo's experiment exactly as he did it, and thereby to gain diachronic historical insight into what the past was actually like.

Einstein and Galileo operating the Morrises' instrument.

Others have been what we might call "celebratory" re-enactors, memorialising the mighty deeds of a scientific culture hero. Their approach is anachronic; they accept as given a particular interpretation of Galileo's result, the interpretation which is important and accepted today. They see Galileo as the giant who first saw this truth, but they unavoidably present him in caricature. When Bezzuoli painted his fresco, the caricature was always grandiose and adulatory: E pur si muove! Today it may be humourous and folksy, even deliberately absurd, in presentations meant to engage a jaded and anti-scientific public. Either way, both the mythic Galileo and his discovery are viewed from the vantage point of the present, the exact opposite of the historians' approach.

Anachronic versions of science history are often intended to be educational: they try to fix some basic data about both science and history in the viewer's mind, deliberately simplifying the context. There is much to be said for this, of course, and yet there is also something more than a bit condescending about it. Nina Simon of the Santa Cruz Museum of Art and History has written a perceptive essay about this issue on her blog "Museum2.0", including the graphic below. It depicts a Galileo re-enactor at an American science-museum in 2010:

These two extremes, and even the gradations between them, are however not typical of re-enactments in this particular case. The inclined plane experiment (and its cousin, the "Tower of Pisa" falling-body experiment discussed last time) are usually replicated in one of two contexts: high-school and introductory-level university physics courses, or very sophisticated experimental-gravitation research programmes. Both of these are what I will define shortly as cenochronic re-enactments. In today's installment of the blog, we will focus on the educational uses of Galileo.

Consider the following two videos, both presumably student lab-reports of some kind. The first is a (relatively) "diachronical" replication of the inclined-plane experiment, using equipment which Galileo would have instantly recognised (at least until it comes time to draw the graph); the second is unabashedly "anachronical", down to the car-shaped rolling-things.

This is of course an instructional experiment, not a true historical simulation, and both versions of it are meant to convey "what Galileo discovered" more than how he discovered it. Indeed, one could teach both labs without mentioning Galileo at all; although this would greatly diminish the human interest of the experiment (and make the use of an archaic timer in the first version seem rather peculiar), it would not alter the value of the scientific information imparted.

In my own experience teaching labs very like this to undergraduates, neither the low-tech nor the high-tech version (much as I confess to preferring the former) has any guarantee of success. The natural tendency of students is to follow laboratory directions like the steps in a magic ritual, and whether those steps involve them in the intricacies of primitive water-clocks or of sensitive photogates does not much matter. The key to a pædagogically successful replication is overcoming this attitude and somehow forcing the students to think about what they are doing, as Galileo must certainly have thought.

One way to achieve this, although I have not personally had the opportunity to try it, would be to begin with very crude versions of the experiment using the simplest possible materials, making no attempt at accuracy. Once the general parameters of the experiment are understood and some of the difficulties recognised, one could proceed to introduce more sophisticated equipment, either "period-accurate" or modern -- or, indeed, a combination -- with the students themselves inventing at least some of the apparatus. Finally, one might do both of the versions shown on the videos above, and compare them with one another and with one's own previous work. After doing this, one would have a strong sense of how things behave rolling down an inclined plane, and of how this does or does not agree with Aristotle's and Galileo's theoretical scenarios (presented in parallel to the experimental project).

A fine, if rather time-intensive, teaching strategy, perhaps -- but what does it have to do with the history of science? Where is Galileo? I would answer that he is at the lab bench. He becomes the students' colleague: he and the students are together investigating the properties of rolling bodies, using whatever materials either may be able to access. As in the purely diachronic approach, Galileo's experiments are replicated by following his own words; as in the anachronic, the emphasis is on the phenomenon, not on the experimenter. But after following his words, one seeks to go beyond them, and in looking at Nature and the same phenomena which interested Galileo, one meets Galileo as someone engaged in the same intellectual exploration as oneself -- in other words as a friend.

I call this attitude "cenochronic". The Greek word κoινóς ("koinos", usually Latinised "cœnus" or, with the decline of ligatures, "cenus") means primarily "common", but also "new" and "modern". Many of its English derivatives are geological. The "Cenozoic" is our "common era" when "new" but now "common" forms of life -- the birds and mammals -- became dominant; its epochs, too, end in "-cene", from the Palæocene ("Ancient Modern") up to the Pleistocene ("Most Modern") and Holocene ("Completely Modern"). There is also "Koinê", the dialect otherwise called "New Testament Greek" after the most famous literary work to be composed in it: Koinê was (in its day) the "new and modern" version of Greek used as a "common" language everywhere in the ethnically diverse Græco-Roman world and by the "common" people especially. In the 1950s some political and theological radicals tried to bring yet another derivative into English -- "koinonia", the Greek word for "community" -- but it does not seem to have caught on.

The "cenochronic" approach to history, then, is one which considers the past and present as occupying a "common" time, so that the past is in a way "new" and "modern" (and the present is in a way ancient). Galileo is our contemporary.

The cenochronic historian takes seriously the cliché about the past being another country. In dealing with a country not one's own, one recognises both that its inhabitants are foreigners with their own culture, and that they are people sharing a universal humanity. To overstress their otherness dehumanises them, whether it leads to their idealisation (as Noble Savages, etc.) or demonisation. On the other hand, to overstress similarities can lead to grave miscalculations, even to wars. Everyone recognises this in the arena of international affairs, but few in the arena of history.

Diachronic history treats our ancestors as unknowable aliens, their motives as provincial to inscrutability. Anachronic history looks back at the past from the superior vantage-point of those who (supposedly) know how it all turned out, subordinating historical persons to present knowledge or misleadingly portraying them as mere reflexions of ourselves. Both approaches dehumanise and objectify previous generations.

In the approach which I advocate here, the historian neither attempts the impossible task of forgetting all modern concerns and living within the constraints of an earlier time, nor the easier but less justifiable one of treating the whole of antiquity as a march, triumphal or disappointing, to the present instant. Rather, the historian recognises that persons of every era are, indeed, persons. They have unique but overlapping interests, and they share a common world. Cenochronic history produces something new out of the old times, and brings those old times into modernity again.

We will see next time (still using Galileo's experiment as an example) how this can take us to the very frontiers of knowledge, and thus include future generations as well.

One minute montage of scenes from Philip Glass's opera Galileo Galilei. Note the (surprisingly accurate) inclined-plane re-enactment at 0:22! (Portland Opera, 2012).